This invention relates to the field of pressure switches which may be used in the transmission of an automobile by way of example.
It has been known to use pressure switches in the prior art which work with a controller to control various systems of an automobile such as the transmission mechanism. For example, a controller receives information from pressure switches as to whether the fluid pressure is of a prescribed level and with this information controls certain functions related to the operation of the automobile.
As is shown in FIG. 6, a prior art pressure switch 100 is provided with a switch chamber 103 that has been partitioned by a diaphragm 102 inside of a switch housing 101. A snap action disc member 104 is provided in switch chamber 103 which is connected to plus terminal 105 and which is movable in and out of engagement with a contact member 106 depending upon the pressure of the fluid exerted upon it. When the disc member 104 is in engagement with contact member 106, an electrical signal is transmitted to a controller through connection of negative electrical terminal 107.
In said pressure switch 100 moreover, an oil cavity 100 is provided in housing 101 to receive oil from oil passage 109 to exert pressure on diaphragm 102. An oil pan 108 surrounds switch 100 as reservoir for the transmission use. It is desirable to try to prevent contaminants in the oil such as dust, chips, etc., from entering switch chamber 103. One method is to make the entrance route of the oil from the oil passage 109 to chamber inside of housing 101 a complicated path, for example, a tortuous path flowing around resin cover 111 and gasket 112.
In regard to switch 100, however, there is a need to put switch chamber 103 in communication with oil pan 108 for the purpose of stabilizing the pressure between the two. As a consequence of this, there have been cases where oil enters the switch chamber 103. In such a case, an oil film is produced between snap acting disc 104 and contact terminal 106 with the result that operational characteristics of the switch can change with changes in the viscosity of the oil. That is, the snap action of disc 104 in making contact with terminal 106 will vary with changes in viscosity of the oil.
Accordingly, there are instances where pressure switch 100 cannot transmit a proper pressure signal based upon the oil pressure instantaneously to the controller, especially in low temperature conditions. In the case where pressure switch 100 is mounted on a plate 113 to be apart from oil pan 108, on the other hand, there are design considerations related to strength, dimensional accuracy etc., with a resultant rise in manufacturing costs, in connection with the installation of each switch 100 on plate 113 so as to prevent a possible leak of oil inside of the oil pan 108 onto plate 113 through switch chamber 103.
In short, there is a strong need to prevent the possible encroachment of oil into switch chamber 103 and to minimize the affect of temperature on switch signal accuracy. Further, there is a need for a compact switch that can be manufactured economically and reliably which has superior operational stability.
Accordingly, it is an object of the present invention to provide a fluid pressure responsive switch with a sealed switching chamber to prevent fluid and other debris from entering the switching chamber thereby providing for a highly reliable switch.
It is another object of the present invention to minimize the effects of temperature variation on the operational performance of the switch.
It is yet another object of the present invention to provide for a compact switch with a simple design which can be manufactured economically and reliably.
More specifically, a pressure switch according to the present invention comprises a base electrode which has a central through hole running therethrough, having a top opening and a bottom opening, a terminal member at least a part of which is containing in said through hole which is electrically insulated from the base electrode by a seal member completely sealing the top opening, a curved shaped fluid pressure responsive disc located in said central through hole adapted to snap over center between a first position in which said disc is not in engagement with the terminal member and a second position in which said disc is in engagement with the terminal member in response to being exposed to a fluid pressure of predetermined value, said disc being electrically connected to said base electrode, and a diaphragm member positioned adjacent said disc for transmitting said fluid pressure from an external source to said disc, said diaphragm being in sealing engagement with said base electrode to completely seal closed the bottom opening of said base electrode thereby providing for a sealed chamber in said base electrode.
In accordance with an embodiment of this invention, the switch chamber is sealed in a vacuum state.
Additional objects and features of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and articles particularly pointed out in the appended claims.